title: HLA class II polymorphism in the Ticuna of Brazil: evolutionary implications of the DRB1*0807 allele.
abstract: The alleles at the HLA class II loci HLA-DRB1, DQA1, DQB1 and DPB1 were determined for 49 individuals of the Ticuna, a Native South American population living in Brazil, using PCR/SSO probe hybridization and DNA sequencing. A newly described DRB1*08 variant, DRB1*0807, which has previously been reported only in native Colombians and contemporary Brazilians of African and Caucasian descent, was identified in the Ticuna at a high frequency (f=0.225). Because *0807 has been observed only in South American populations, we propose that it was generated from a parental *0802 allele recently, after the isolation of various Native South American populations, and infer that the DRB1*0807 allele was generated by a C to T change at codon 57 (Asp-->Val, GAT-->GTT) from the ancestral *0802. This inference is supported by the sequence of a complex VNTR in the second intron of the DRB1 gene. The DPB1 alleles *0401, *0402 and *1401 constituted 76% of the observed Ticuna DPB1 alleles (f=0.166, 0.427 and 0.166 respectively). In addition, the DPB1 allele *3501, which has been observed in a few other Native South American groups, was observed at a frequency of 0.053 and may have been generated from the putative ancestral allele *1401 allele in South America. The DRB1 and DPB1 allele frequencies for the Ticuna deviate from expected Hardy-Weinberg equilibrium proportions, while DQA1 and DQB1 allele frequencies do not. When this deviation, which involves an observed excess of DRB1*0807 heterozygotes, is considered with the high frequency of the DRB1*0807 and DPB1*1401 alleles, we infer that native South American populations may have been under selection pressure for increased allele diversity.
authors.affiliation: Department of Molecular and Cell Biology, University of California at Berkeley, USA.
authors.forename: S J
authors.initials: SJ
authors.lastname: Mack
authors.forename: H A
authors.initials: HA
authors.lastname: Erlich
mesh_terms: D000349:Africa; D000483:Alleles; D001938:Brazil / Q000208:ethnology; D002874:Chromosome Mapping; D004272:DNA, Mitochondrial; D019143:Evolution, Molecular; D005787:Gene Frequency; D006682:HLA-DP Antigens / Q000235:genetics; D059868:HLA-DP beta-Chains; D006683:HLA-DQ Antigens / Q000235:genetics; D059848:HLA-DQ alpha-Chains; D059866:HLA-DQ beta-Chains; D006684:HLA-DR Antigens / Q000235:genetics*; D059811:HLA-DRB1 Chains; D006239:Haplotypes; D006720:Homozygote; D006801:Humans; D007199:Indians, South American / Q000235:genetics*; D015810:Linkage Disequilibrium; D008957:Models, Genetic; D011110:Polymorphism, Genetic
chemical_list: D004272:DNA, Mitochondrial; D006682:HLA-DP Antigens; D059868:HLA-DP beta-Chains; C071170:HLA-DPB1 antigen; D006683:HLA-DQ Antigens; D059848:HLA-DQ alpha-Chains; D059866:HLA-DQ beta-Chains; C069050:HLA-DQA1 antigen; C069051:HLA-DQB1 antigen; D006684:HLA-DR Antigens; D059811:HLA-DRB1 Chains